Ion channeling studies of GaN layers on c-oriented sapphire

The successful growth of epitaxial GaN films by metal organic vapor phase epitaxy (MOVPE) or gas source molecular beam epitaxy (GSMBE) has opened up new applications in short wavelength photonic devices for displays and optical data storage systems. The large lattice mismatch of 14% between GaN and sapphire, usually used as the substrate, and the different thermal expansion coefficients generally lead to high densities of structural defects. In this paper we investigate the defect structure of MOVPE- and GSMBE-grown GaN layers on sapphire by Rutherford backscattering and ion channeling measurements. In addition to axial c-axis channeling, which reveals chi(min) values as low as 1.2%, channeling measurements along the (2 (1) over bar (1) over bar 0) and (1 (1) over bar 0 0) crystal planes were performed in order to improve the sensitivity to dechanneling by crystalline defects. Angular scans around the c-axis indicate clearly the hexagonal symmetry of the GaN lattice. Dechanneling results were compared to observations of defects by transmission electron microscopy (TEM). This comparison suggests that the cross-section of dechanneling by edge dislocations is about a factor of 4 larger than the dechanneling cross-section of screw dislocations. (C) 1998 Elsevier Science B.V.